Charles Bensinger/ Renewable Energy Partners of New Mexico and DOE/NREL

Biofuels

Fuel derived from biological material, or biofuel, is an appealing renewable alternative to fossil fuels. It is sustainable, reduces U.S. dependence on imported oil, and potentially generates lower greenhouse gas emissions than fossil fuels. However, its viability may depend greatly on government policies, including agricultural subsidies and requirements to reduce CO2 emissions, as well as market prices of other fuels.

One drawback of corn ethanol production is that it requires a large amount of land and fresh water, along with inputs of fertilizers and energy.

Grain-based ethanol—now chiefly made from corn and already commercially deployed—is at best a transitional technology, according to the AEF committee. One drawback of corn ethanol production is that it requires a large amount of land and fresh water, along with inputs of fertilizers and energy. This results in potential competition with food sources for land use and with other industrial and commercial needs for fresh water. In addition, the current technology is very energy intensive—two-thirds of the energy value of corn ethanol is used just to produce the fuel—and most of that energy comes from fossil fuel-based electricity or heating, offsetting much of the benefit.

Nonetheless, corn-grain ethanol is already replacing a small amount of fossil-fuel use in vehicles. The federal government has an aggressive program to encourage its production. As a result, in 2005 about 4 billion gallons of fuel ethanol mixed with gasoline hit the domestic market. But in the same year, the United States consumed about 140 billion gallons of gasoline and 40 billion gallons of diesel fuel, so ethanol accounted for only a small percentage of the total gasoline pool.

Many experts believe that ethanol-based biofuels will not provide much benefit until the conversion technology is fully developed to use cellulose (as found in trees and grasses) for the raw material instead of corn or sugar cane. In fact, the Energy Independence and Security Act of 2007 stipulates that by 2022 the United States must produce 21 billion gallons of advanced biofuels, such as cellulosic ethanol. Other technologies readying for deployment beyond 2020 include algal biodiesel, a fuel produced from algae, and biobutanol, a fuel currently derived from sugars and starches, but potentially from cellulosic biomass. Unlike ethanol, which has to be transported by trucks and barges, algal biodiesel and biobutanol can be transported via existing infrastructure, such as petroleum pipelines. However, significant technical and cost challenges must still be overcome to ensure a major role for either of these biofuels in our energy future.

Even with this increased focus on biofuels, it is uncertain how much projected gasoline consumption can be replaced in the next few decades. Experts predict that an aggressive program to develop these technologies would result, by 2035, in a 1.7 million barrels per day contribution of biofuels to the nation’s current 20 million barrels per day consumption of petroleum. Furthermore, biofuels contain carbon, and although they may burn “cleaner” than oil-derived fuels, they would not completely eliminate CO2 emissions. That situation could be different if the crops used to produce the biofuels were grown sustainably, drawing as much carbon from the atmosphere during their growth as they release when burned. If the biofuels were also burned in an electric power plant where CO2 was captured and sequestered, the entire process could be a net carbon absorber.